The present invention relates to wastewater treatment systems, and deals more specifically with an improvement to a conventional septic tank system with a single holding tank, and associated leaching field, wherein the effluent from the leaching field is further processed in a porous bed that includes at least one horizontally disposed infiltration device, or in-drain, and wherein a liquid soap solution is periodically injected into this in-drain from a source at or above the level of the holding tank to take advantage of biological activity of the nitrates in this anaerobic atmosphere and thereby remove phosphors, viruses, bacteria and waste products in the system from the kitchen and laundry area. The liquid soap contains soluble organic carbon that serves as an anaerobic electron donor to denitrify the effluent nitrogen gas from such effluent.
Prior art sewage treatment systems of the type adapted to separate effluent, as between black water and gray water, are known. See for example my prior U.S. Pat. No. 4,465,594 issued Aug. 14, 1984 wherein the black water and gray water effluent are separated and fed to separate holding tanks. These effluents are then recombined in a denitrification process under anaerobic conditions.